1. Field of the Invention
This invention relates to the use of selected mixtures of, on the one hand, end-capped and, on the other hand, non-end-capped polyethylene glycol ethers as alkali-stable foam-inhibiting additives, which can be homogeneously formulated into aqueous highly concentrated alkali solutions, in low-foaming cleaning products. The active-substance mixtures according to the invention are particularly suitable for use as foam inhibitors for bottle washing and for so-called cleaning in place (CIP). The invention seeks to provide auxiliaries of the type mentioned which combine high effectiveness with physiological harmlessness and biological degradability. In addition, the invention addresses the problem of, on the one hand, optimizing the performance profile of the auxiliaries used in practical application and, on the other hand, providing selected polyethylene glycol ethers of the type mentioned which ensure improved formulatability of these auxiliaries in marketable concentrate form.
Low-foaming cleaning products for institutional and industrial use, particularly for cleaning metal, glass and ceramic surfaces, generally contain foam-suppressing additives which are capable of counteracting unwanted foaming. The foam-suppressing auxiliaries generally have to be used because the soil particles detached from the substrates and collecting in the cleaning baths act as foam generators. However, the cleaning products themselves may contain constituents which give rise to unwanted foaming under the particular working conditions. One example of such constituents are the widely used anionic surfactants.
2. Discussion of Related Art
One class of highly effective and, at the same time, biologically degradable foam inhibitors is described in DE-OS 33 15 951 which relates to the use of end-capped polyethylene glycol ethers corresponding to formula (I) R.sub.1 O--(CH.sub.2 CH.sub.2 O)--.sub.n R.sub.2 in which R.sub.1 is a linear or branched alkyl or alkenyl radical containing 8 to 18 carbon atoms, R.sub.2 is an alkyl radical containing 4 to 8 carbon atoms and n is an integer of 7 to 12. A product of this type, wherein R.sub.1 is a C.sub.12-18 fatty alcohol radical, R.sub.2 is the n-butyl radical and n is the number 10, has proved to be particularly successful in practice.
By slightly modifying the structure of the fatty alcohol polyethylene glycol ethers mentioned, it is possible in particular to provide for improved operation at relatively low temperatures, for example of the order of room temperature or only slightly elevated temperatures. DE-OS 38 00 493 relates to the use of polyethylene glycol ethers corresponding to general formula (I) above, in which R.sub.1 is a linear or branched alkyl or alkenyl radical containing 20 to 28 carbon atoms, R.sub.2 is an alkyl radical containing 4 to 8 carbon atoms and n is a number of 6 to 20. In this case, the crucial modification lies in the use of relatively long-chain radicals R.sub.1. These end-capped polyglycol ethers are also distinguished by high stability to acids and alkalis. Their foam-inhibiting effect in alkaline and neutral cleaning liquors is enhanced in the described sense, in addition to which they satisfy legal requirements in regard to biodegradability.
It is known that nonionic surfactants based on polyglycol ether compounds cannot readily be incorporated in aqueous, strongly alkaline formulations. They easily form a phase separate from the aqueous phase and, accordingly, require the use of solubilizers. Known effective solubilizers, particularly for strongly alkaline cleaning formulations, are alkyl mono- and/or oligoglucosides which, for ecological reasons also, must be a preferred class of compounds for the particular field in question.
Thus, EP-A2-0 202 638 describes a liquid cleaning concentrate for strongly alkaline cleaning formulations consisting of end-capped fatty alcohol glycol ether compounds containing mixed oligoalkoxide functions together with a combination of three solubilizers which is said to ensure homogeneous formulation in aqueous, strongly alkaline solutions. One of these solubilizers is an alkyl monoglucoside and/or alkyl polyglucoside containing 8 to 12 carbon atoms in the alkyl part and 1 to 6 glucose units. U.S. Pat. No. 4,240,921 also describes an aqueous concentrate containing 10 to 35% by weight alkali metal hydroxide, 10 to 50% by weight of a mixture of a polyoxypropylene/polyoxyethylene condensate, an etherified ethoxylated alcohol and an alkyl glucoside as an alkaline detergent concentrate for bottle washing. The disadvantage of these preparations, particularly in the context of the last-mentioned teaching, is that they foam too vigorously in practical application, particularly through the presence of the alkyl glucoside. In addition, phase separation occurs at high alkali contents.
The problem addressed by the present invention was to make it possible by "fine tuning" and optimization of the choice of the polyethylene glycol ether compounds used to obtain mixtures which would be distinguished by effects of particularly high quality when used as foam inhibitors and which would be accessible to this optimization of their effect both at comparatively low temperatures, i.e. for example at temperatures of the order of 20.degree. C., and at the elevated temperatures typically applied in practice, for example in the range from about 60.degree. to 70.degree. C. Another problem addressed by the invention was to enable these auxiliaries to be formulated in strongly alkaline, highly concentrated aqueous solutions to single-phase systems over the temperature range important in practice, i.e. for example from about 20.degree. to 70.degree. C.